Cells of the immune system alter patterns of gene expression in response to extracellular and intracellular signals. A group of polypeptides, designated cytokines or lymphokines, which affect a range of biological activities in several cell types, are among the most important of these signals. While many cell types in the immune system secrete cytokines, the T helper (Th) lymphocyte is the major source of these polypeptides. More than a decade ago it was discovered that Th cells differentiate into two distinct subsets, Th1 and Th2, upon T cell receptor engagement, defined both by their distinct functional abilities and by unique cytokine profiles (Paul and Seder, 1994, Cell 76, 241-251; Mosmann and Coffman, 1989, Annu. Rev. Immunol. 7, 145-173; Mosmann et al., 1986, J. Immunol. 136, 2348-2357; Snapper and Paul, 1987, Science 236, 944-947). Th1 cells mediate delayed type hypersensitivity responses and macrophage activation while Th2 cells provide help to B cells and are critical in the allergic response (Mosmann and Coffman, 1989, Annu. Rev. Immunol. 7, 145-173; Paul and Seder, 1994, Cell 76, 241-251; Arthur and Mason, 1986, J. Exp. Med. 163, 774-786; Paliard et al., 1988, J. Immunol. 141, 849-855; Finkelman et al, 1988, J. Immunol. 141, 2335-2341). The evidence that Th1 cells directed cell-mediated immunity while Th2 cells contributed to humoral responses fit nicely with the observations that an organism tends to mount either a cell-mediated or humoral response, but not both, in response to pathogens. These functional differences between the Th subsets can be explained most easily by the activities of the cytokines themselves. IFN-γ is the “signature” cytokine of Th1 cells although Th1 cells also produce IL-2, TNF and LT. The corresponding “signature” cytokine for Th2 cells is IL-4. Th2 cells also secrete IL-5, IL-6, IL-9, IL-10 and IL-13.
Upon encountering antigen, the naive CD4+ T helper precursor (Thp) cell enacts a genetic program that ultimately sends it down a Th1 or Th2 lineage. While it is clear that polarization can be achieved by manipulating the antigen and costimulatory signals i.e. the “strength of signal” received by the Thp (Constant and Bottomly, 1997. Annu. Rev. Immunol. 15, 297-322), the most potent inducers of effector Th cells are undoubtedly the cytokines themselves. IL-4 promotes Th2 differentiation and simultaneously blocks Th1 development, an effect that is mediated via the Stat6 signaling pathway. Thus, mice that lack IL-4 or Stat6, fail to develop Th2 cells (Kopf et al., 1993, Nature 362, 245-248; Kuhn et al., 1991, Science 254, 707-710; Kaplan et al., 1996, Immunity 4, 313-319; Shimoda et al., 1996, Nature 380, 630-633; Takeda et al., 1996, Nature 380, 627-630). In contrast, IL-12, IL-18 and IFN-γ are the cytokines critical for the development of Th1 cells (Hsieh et al., 1993, Science 260, 547-549; Okamura et al., 1995, nature 378, 88-91; Gu et al., 1997, Science 275, 206-209; Meraz et al., 1996, Cell 84, 431-442; Magram et al., 1996, Immunity 4, 471-481). IFN-γ acting via the Stat1 pathway (Meraz et al., 1996, Cell 84, 431-442), and IL-12, acting via the Stat-4 signaling pathway (Jacobson et al., 1995, J. Exp. Med. 181, 1755-1762) together promote the differentiation of Th1 cells and block commitment to the Th2 lineage (Szabo et al., 1995, Immunity 2, 665-675; Szabo et al., 1997, J. Exp. Med. 185: 817-824). Mice deficient in IL-12 or Stat4 do not have Th1 cells (Magram et al., 1996, Immunity 4, 471-481; Takeda et al., 1996, Nature 380, 627-630; Shimoda et al., 1996, Nature 380, 630-633). Another important Th1-inducing cytokine is IL-18, whose receptor is related to the IL-1 receptor family (Cerretti et al., 1992, Science 256, 97-100). Mice lacking IL-18 have defective in vivo Th1 responses (Takeda et al., 1998, Immunity 8, 383-390) and both IL-12 and IL-18 regulate IFN-γ expression (Barbulescu et al., 1998, Eur. J. Immunol. 27, 1098-1107; Robinson et al., 1997, Immunity 7, 571-581; Ahn et al., 1997, J. Immunol. 159, 2125-2131). The cytokines themselves, then, form a positive and negative feedback system that drives Th polarization (Powrie and Coffman, 1993, Immunol. Today 14, 270-274; Scott, 1991, J. Immunol. 147, 3149; Maggi et al., 1992, J. Immunol. 148, 2142; Parronchi et al., 1992, J. Immunol. 149, 2977; Fargeas et al., 1992, Eur. J. Immunol. 149, 2977; Manetti et al., 1993, J. Exp. Med. 177, 1199; Trinchieri, 1993, Immunol. Today 14, 335-338; Macatonia et al., 1993, Immunol. 5, 1119; Seder et al., 1993, Proc. Natl. Acad. Sci. USA 90, 10188-10192; Wu et al., 1993, J. Immunol. 151, 1938; Hsieh et al., 1993, Science 260, 547-549) (reviewed in (Seder and Paul, 1994, In Annual Review of Immunology, Vol. 12, 635-673; Paul and Seder, 1994, Cell 76, 241-251; O'Garra, 1998, Immunity 8, 275-283).
Over the last few years, significant progress has been made in identifying the transcription factors that control the transition of a Thp to a Th2 cell as evidenced by the capacity of such factors to drive IL-4 production reviewed in (Glimcher and Singh, 1999 Cell 96, 13-23; Szabo et al., 1997, Current Opinions in Immunology 9, 776-781). The provision of three distinct proteins, the c-Maf proto-oncogene, the transcription factor Nuclear Factor of Activated T cells (NFAT), and a novel nuclear antigen, NFAT-Interacting Protein 45 kD (NIP45), have been shown to confer on a non-T cell the ability to produce endogenous IL-4 (Hodge et al., 1996, Science 274, 1903-1905; Ho et al., 1998, J. Exp. Med. 188:1859-1866). These factors and others such as GATA-3 (Zheng and Flavell, 1997, Cell 89, 587-596) and Stat6 clearly can drive the production of IL-4, and therefore the development of Th2 cells, both in vitro and in vivo.
In contrast, little is known about the molecular basis of Th1 differentiation. For example, the only known transcription factors whose absence results in a failure to generate Th1 cells are Stat4 (Thierfelder et al., 1996, Nature 382, 171-174; Kaplan et al., 1996, Nature 382, 174-177) and IRF-1 (Lohoff et al., 1997, Immunity:681-689; Taki et al., 1997, Immunity 6:673-679), neither of which is Th1-specific. The Ets family member ERM which is induced by IL-12 in a Stat4-dependent manner has recently been reported to be Th1-specific but it does not affect the production of Th1 cytokines (Ouyang et al, 1999, Proc. Natl. Acad. Sci. 96:3888). The absence of Th1 cells in Stat4 deficient mice is secondary to the failure of IL-12 to drive the Th1 program while the lack of Th1 cells in IRF-1 deficient mice is likely due to its direct effect in controlling transcription of the IL-12 gene (Lohoff et al., 1997, Immunity 6: 681-689; Taki et al, 1997, Immunity 6:673-679). However, some of the signaling pathways upstream of such putative Th1-specific regulatory factors are beginning to be elucidated. The p38 kinase is one such signaling molecule as demonstrated by the ability of constitutively activated MAP kinase kinase 6 (MKK6) to boost IFN-γ production. Conversely, overexpression of a dominant negative p38 MAP kinase or targeted disruption of Jnk2 or Jnk1 reduces Th1 responses (Rincón et al., 1998, EMBO J. 17, 2817-2829; Yang et al, 1998, Immunity 9, 575-585; Dong et al., 1998, Science 282, 2092-2095). The JNK signaling pathway might affect Th development by a direct effect on the transcription of the IFN-γ gene, but this has not been shown. For example, the ATF-2 and AP-1 transcription factors are both substrates of JNK kinases and these factors as well as NFκB and Stat4 proteins are known to bind to sites in the IFN-γ promoter (Zhang et al, 1998, Immunol. 161, 6105-6112; Ye et al., 1996, Mol. Cell. Biol. 16:4744; Barbulescu et al., 1997, Eur. J. Immunol. 27, 1098-1107; Sica et al., 1997, J. Biol. Chem. 272, 30412-30420). The production of IFN-γ is, however, normal in mice lacking ATF-2. Because cytokines are critical in the development of Th1 and Th2 cells and, thereby, in determining whether an immune response will be primarily cellular or humoral, compositions and methods for modulating the production of Th1 and/or Th2 cytokines would be of tremendous benefit in modulating the immune response.